The present invention relates to a new and improved drafting mechanism for spinning machines, in particular for air jet spinning machines.
In its more particular aspects, the drafting mechanism of the invention is of the type comprising at least one delivery roller pair together with a further roller pair located upstream from the delivery roller pair considered in the direction of movement of the fiber sliver or the like, the rollers of the further roller pair being provided with respective aprons for guiding the fiber sliver, the exit opening of the apron pair being so arranged in relation to the nip line of the delivery roller pair that the fiber sliver undergoes at least one diversion or deflection in the region between the exit opening and the nip line.
In the course of drafting short staple fiber sliver to yarn or the like , with increasing fineness of the yarns there is increasingly present the necessity to guide the fibers as far as possible between the nip points of a drafting passage.
This requirement is especially important in so-called jet spinning processes, in which drawing frame sliver is drawn by a drafting mechanism having only three or two drafting zones into feed material ready for formation of yarn by the jet spinning process.
In addition, in the jet spinning method, the air flows prevailing at the circumference of the delivery rollers of the drafting mechanism, caused by the high peripheral speeds of approximately 150 m/min., can cause edge fibers to be separated or spread out from the body of fibers shortly before being grasped by the nip of the delivery roller pair. This phenomenon results either in loss of fibers or irregularity in the yarn. The separation or spreading of the fibers occurs in the converging space or region of the delivery roller pair, that is in the region of the entry zone to the nip of the two delivery rollers. In this zone, the peripherally directed air flows or air streams of the rotating rollers are diverted to air flows or air streams directed substantially parallel to the axes of the rollers, which causes the aforementioned undesirable separation and/or spreading of the edge fibers. Since the separation and spreading of the fibers as a result of these airstreams is highly variable, this results in the already mentioned irregularity in the yarn.
In order to avoid this, it is proposed in German Published Patent Specification No. 3,039,149, to displace the exit opening of the apron drafting mechanism relative to the nip location of the delivery rollers in a direction normal to the "path of the fiber flow" (see claim 2 and FIG. 2 of the just mentioned German Patent Specification). Through this displacement, the fiber path is supposed to evade the transverse air flows, that is to say, this fiber path to a certain extent is to bypass such transverse air flows, in order to reach the nip in the region close to the surface of the adjacent roller.
The disadvantage of this system is that the peripherally directed air flow of the adjacent roller flows through the fiber sliver from one side thereof and thus causes transverse bending and from which bent fiber sliver fiber ends are spread-out in the transverse flow zone, so that the disadvantage which was to be eliminated is reproduced in another manner.